Don’t remove units in flex-basis value for (-ms-)flex shorthand

[Didel]

According to issue #362 this was reported and fixed in an earlier version of CSSO. However, it looks like this is (partially) broken again.

The main work-around listed on Flexbugs (using 0% as a value, see https://github.com/philipwalton/flexbugs#4-flex-shorthand-declarations-with-unitless-flex-basis-values-are-ignored ) is actually not working with the current version (4.0.2). We should aim to fix this, as the work-around is probably well-known by now and because it is suggested it is the first thing developers will try to prevent the problem. A value of 0px is working as you'd expect (i.e. the unit is not removed). Also, the discussion in the original issue concludes:

Decision: we should remove unit removal for -ms-flex only

Which is not happening, the behaviour is the same for both flex and -ms-flex. In the example below, I actually expect that the output would be the same as the input, or at least for the -ms-flex uses.

Given the following input:

.flex {
    flex: 1 0 0;
}

.flex-pct {
    flex: 1 0 0%;
}

.flex-px {
    flex: 1 0 0px;
}

.ms-flex {
    -ms-flex: 1 0 0;
}

.ms-flex-pct {
    -ms-flex: 1 0 0%;
}

.ms-flex-px {
    -ms-flex: 1 0 0px;
}

I get the following output:

.flex {
    flex: 1 0 0
}

.flex-pct {
    flex: 1 0 0
}

.flex-px {
    flex: 1 0 0px
}

.ms-flex {
    -ms-flex: 1 0 0
}

.ms-flex-pct {
    -ms-flex: 1 0 0
}

.ms-flex-px {
    -ms-flex: 1 0 0px
}

Originally posted by @Didel in #362 (comment)